Transaction correlation is the functionality that maintains the business transaction context across all tiers—servers—traversed by a distributed transaction. The tiers may be built on platforms other than Node.js. For example, Java, .NET, and PHP tiers may participate in a distributed business transaction in which a Node.js tier participates, as originating, continuing or terminating tiers in the transaction.

The Node.js Agent APIs provide facilities for managing transaction correlation among various transactions, which may be custom or automatically-detected.

While the Splunk AppDynamics default auto-detection mechanism obtains transaction correlation information from an incoming HTTP request, the Node.js Agent APIs allow you to obtain this information from other sources, such as a custom field in a Redis cache entry, and to supply it to your custom transactions. You can use the APIs to support forward correlation by supplying transaction correlation information on exit calls that you make to downstream transactions.

A downstream transaction starts after its immediate upstream transaction makes its exit call. That call could be a direct exit call to the next tier or a call to a backend service that does some processing, such as publishing a message onto a queue.